Regnier M, Martyn D A, Chase P B
Department of Physiology and Biophysics, University of Washington, Seattle 98195, USA.
Biophys J. 1996 Nov;71(5):2786-94. doi: 10.1016/S0006-3495(96)79471-7.
To examine if the Ca2(+)-binding kinetics of troponin C (TnC) can influence the rate of cross-bridge force production, we studied the effects of calmidazolium (CDZ) on steady-state force and the rate of force redevelopment (ktr) in skinned rabbit psoas muscle fibers. CDZ increased the Ca2(+)-sensitivity of steady-state force and ktr at submaximal levels of activation, but increased ktr to a greater extent than can be explained by increased force alone. This occurred in the absence of any significant effects of CDZ on solution ATPase or in vitro motility of fluorescently labeled F-actin, suggesting that CDZ did not directly influence cross-bridge cycling. CDZ was strongly bound to TnC in aqueous solutions, and its effects on force production could be reversed by extraction of CDZ-exposed native TnC and replacement with purified (unexposed) rabbit skeletal TnC. These experiments suggest that the method of CDZ action in fibers is to bind to TnC and increase its Ca2(+)-binding affinity, which results in an increased rate of force production at submaximal [Ca2+]. The results also demonstrate that the Ca2(+)-binding kinetics of TnC influence the kinetics of ktr.
为了研究肌钙蛋白C（TnC）的Ca2+结合动力学是否会影响横桥力产生的速率，我们研究了平静素（CDZ）对去皮肤的兔腰大肌纤维稳态力和力再发展速率（ktr）的影响。在次最大激活水平下，CDZ增加了稳态力和ktr的Ca2+敏感性，但ktr的增加程度超过了仅由力增加所能解释的范围。这一现象发生时，CDZ对溶液ATP酶或荧光标记的F-肌动蛋白的体外运动性没有任何显著影响，表明CDZ没有直接影响横桥循环。CDZ在水溶液中与TnC紧密结合，通过提取暴露于CDZ的天然TnC并用纯化的（未暴露的）兔骨骼肌TnC替代，可以逆转其对力产生的影响。这些实验表明，CDZ在纤维中的作用方式是与TnC结合并增加其Ca2+结合亲和力，这导致在次最大[Ca2+]时力产生速率增加。结果还表明，TnC的Ca2+结合动力学影响ktr的动力学。
